1. Field of the Invention
This invention relates to a primer composition which provides the surface of a plastics substrate with a top-coating having high wear resistance, surface hardness, heat resistance and chemical resistance as well as to a process for producing a coated product characterized by using such primer composition. More particularly, this invention relates to a primer composition comprising a specific diepoxy compound dissolved in an organic solvent and to a process comprising coating the surface of a plastics substrate with the primer composition, heating the primer-coated plastics substrate to provide a dry prime coating, and then coating a top-coating paint over the dry prime coating to thereby prepare a desired coated product.
2. Description of the Prior Art:
Of a variety of transparent plastic molded articles in current use, those molded from acrylic or methacrylic resins are lightweight, have high mechanical properties and an esthetically appealing appearance. But unfortunately, these resins are inferior to metals and other inorganic materials in respect of wear resistance, surface hardness, heat resistance and chemical resistance. A polycarbonate resin has relatively high wear resistance and surface hardness, but not so high as to withstand practical use. Therefore, many attempts have heretofore been made to improve the characteristics of the surface of acrylic resin, methacrylic resin, polycarbonate resin and other transparent plastics.
The inventors of this invention have also proposed several techniques for improving the surface hardness, wear resistance, heat resistance and chemical resistance of a transparent plastic molded article. To be more specific, as a result of studies on the coating of a silicone-containing polymer applied to a transparent plastics substrate, the present inventors have successfully prepared a series of silicone-containing thermosetting resin compositions that are capable of providing the surface of a transparent plastics substrate with a hardened film which satisfies the requirements of high wear resistance, surface hardness, heat resistance and chemical resistance, and these resin compositions are the subject of pending Japanese patent applications.
However, the coating of these silicone-contaning resin compositions does not always adhere strongly to the treated plastics substrate. For instance, a polycarbonate resin or polymethyl methacrylate resin is easily attacked by a monomer or a solvent and turns cloudy upon contact with a coating agent that contains such monomer or solvent. A polymethyl methacrylate resin as well as polycarbonate resin has low affinity for a vinyl compound and silicone compound; hence only low adhesive bond strength is obtained between the plastics substrate and the coating. It is, therefore, necessary that some plastics substrate be treated with a primer to form a prime coating before they are given the final coating.